1. Field of the Invention
This invention relates to a rotatable coupler for electrically connecting two RF or UHF coaxial cables together. The coupler allows for relative rotation between the cables, thereby preventing damaging torques from occurring during use.
2. Description of Related Art
There are many environments in which a coaxial cable used to transmit RF or UHF signals is subject to intermittent or continual rotational forces as a part of its normal duties. For instance, a long coaxial cable is normally coiled during storage and transport. When connecting such a coaxial cable to an antenna or to another coaxial cable in a coaxial line, each coaxial cable is uncoiled. As each is uncoiled to add it to the line, straightening the cable produces rotational torques within it and applies them to all of the cables connected to it. Between their ends, coaxial cables are designed to withstand these forces, but they are vulnerable at their ends where they connect to each other or to intermediate connectors. Without some way of eliminating the rotational forces or of relieving their effects, at least one of the cables along the line will inevitably fail, requiring the line to be inspected to determine which cable has failed and requiring the subsequent replacement thereof. When in the field, such a failure is never convenient and is always expensive.
A prior art cable connector 10 typical of those currently used in the field is shown in FIG. 3 in a perspective view, partly in section. Connector 10 releasably joins a first cable 12 and a second cable 14.
Both cables 12 and 14 are coaxial cables such as are commonly used to transmit RF or UHF signals. The structural configurations of both cables 12 and 14 are in most respects the same, so common reference numerals are used to denote corresponding elements. Cables 12 and 14 comprise a central lead 16 and a conductive outer sleeve 18 (see the portion of cable 14 which is in section), the conductors 16 and 18 being separated and supported by an insulative material 20 (cable 12). A tough but flexible skin 22, reinforced by a helical wire 24 imbedded therein (cable 14), protects the innards of cables 12 and 14 from physical damage during transport, storage, and use. Conductive ferrules 26 are fixed to the ends of cables 12 and 14 to effect signal transfer from one cable to another.
Connector 10 comprises a cylindrical, metallic extension 28 integral with ferrule 26 of cable 12 and an elongated, metallic, cylindrical ring 30 rotatably attached to ferrule 26 of cable 14. Extension 28 has an externally threaded end 32 which mates with internal threads 34 in cylindrical ring 30, much like the two connecting ends of an ordinary water hose. When extension 28 and cylindrical ring 30 are threadedly connected, a knife-like tip 36 of central lead 16 of cable 14 is forced into and gripped by resilient fingers 38 of central lead 16 of cable 12, thus assuring good conductivity along the central leads. Conductivity through outer sleeves 18 is through extension 28, cylindrical ring 30, and ferrules 26. Each of ferrules 26 have a flange 40 in conductive contact with sleeve 18, as shown in the broken-away portion of cable 14.
When ring 30 is securely joined together with extension 28 via threads 32 and 34, cables 12 and 14 cannot rotate or swivel relative to each other. Any torques on either cable are resisted by the internal structures of the cables. When a failure occurs, it most usually occurs in the area of the juncture of flange 40 and sleeve 18.
Other inventors have addressed problems arising when connecting coaxial cables. Representative are the U.S. Pat. Nos. 3,847,463 to Hayward et al., 4,022,518 to Gattaz, 4,336,974 to Wilson, 4,988,963 to Shirosaka et al., and 5,419,707 to Kelley. While undoubtedly effective for their purposes, to the inventor""s knowledge, they and others like them tend to be complicated, expensive, and have not met with widespread acceptance.
The present invention overcomes the difficulties described above by providing a coupler for a pair of coaxial cables, said coupler permitting good transmission of RF and/or UHF signals while concurrently permitting relative rotation between the cables coupled thereby. As a consequence, both cables are relieved of the stresses normally imposed by the rotational torques suffered by moving the cables, which greatly extends their useful lives.
It is an object of the invention to provide a coupler for coaxial cables which permits relative rotation or swivelling between the cables.
It is a further object of the invention to provide a coupler for coaxial cables which resists linear forces along the line while permitting relative rotation.
It is a further object of the invention to provide a coupler for coaxial cables in which the burden for the rotational and non-linear constraints are carried by the coupler housing structure and not by the electrical components thereof.
It is a further object of the invention to provide a coupler for coaxial cables which effectively transmits the signals therein from one cable to another while permitting easy rotation therebetween.
It is a further object of the invention to provide a coupler for coaxial cables which shields the signals in the coupler as they are transmitted from one coaxial cable to another.
It is a further object of the invention to provide a coupler for coaxial cables which is easy to attach and detach from the cables.
It is a further object of the invention to provide a coupler for coaxial cables which permits adapting the coupler for different input and output connectors on the ends of coaxial cables.
It is a further object of the invention to provide a coupler for coaxial cables which is simple in structure and inexpensive to manufacture.
It is a further object of the invention to provide a coupler for coaxial cables which is small enough that an extensive inventory of couplers and parts can easily be carried into the field.